I. Field of the Invention
The present invention relates to implantable pulse generators and, more particularly, implantable pulse generator headers and the electrical connectors used in the construction of such headers. The present invention also relates to methods for manufacturing electrical connectors for headers for implantable pulse generators.
II. Discussion of Related Art
In medical technology an implanted pulse generator (IPG) may be employed for a variety of purposes. An IPG is a battery powered device designed to deliver electrical stimulation to the body. An IPG is typically an integral component of a surgically implanted system, which includes the IPG, one or more leads and an external programmer. Such systems fall into two broad categories, neuromodulation systems and cardiac rhythm management systems. Neuromodulation systems are used, for example, to provide deep brain stimulation, vagus nerve stimulation, spinal cord stimulation, peripheral nerve stimulation and the like. Such stimulation has proven to be beneficial for the treatment of intractable pain, Parkinson's disease, pelvic disorders and incontinence, sleep apnea, and epilepsy, among other conditions. Cardiac rhythm management systems include heart pacemakers, defibrillators, cardioverters and other forms of devices used to monitor and control heart rhythms.
The IPG is typically implanted within a person's body, usually beneath the clavicle. Leads are then routed through the body between the site to be stimulated and the IPG. The leads are then coupled to the header of the IPG to carry signals between the IPG and the treatment site. The IPG can be calibrated using the external programmer by a physician (such as an electrophysiologist, neurologist or cardiologist) or by a nurse or other trained technician to meet the individual patient's needs. The IPG must be replaced periodically upon battery depletion. Battery depletion can occur within three to five years, though battery life is dependent on individual usage. End of battery life can be reasonably predicted by the use of telemetry between the IPG and the external programming device. This allows the IPG to be replaced prior to battery failure.
As indicated above, one example of an IPG is a heart pacemaker (or artificial heart pacemaker, so as not to be confused with the heart's natural pacemaker), a medical device which uses electrical impulses to regulate the beating of the heart. When the IPG is employed as an artificial heart pacemaker, the IPG is used in combination with a lead comprising a set of electrodes which carry stimulation pulses from the IPG to the heart and electrical signals back from the heart to the IPG which senses and responds to such signals. The primary purpose of a pacemaker is to maintain an adequate heart rate, either because the heart's native pacemaker is not fast enough, or because there is a block in the heart's electrical conduction system. Modern pacemakers are externally programmable and allow the electrophysiologist to select the optimum pacing modes for individual patients. Some IPG devices combine a pacemaker and defibrillator in a single implantable device. Multiple electrodes stimulating differing positions within the heart are often used to improve synchronization of the contractions of the upper and lower and chambers of the heart.
Another type of IPG is an implantable cardioverter-defibrillator (ICD), a small battery-powered electrical pulse generator which is implanted in patients who are at risk of sudden death due to ventricular fibrillation or ventricular tachycardia. The device is programmed to detect cardiac arrhythmia and correct it by delivering a jolt of electricity. In current variants, ICD devices have the ability to treat both atrial and ventricular arrhythmias as well as the ability to perform biventricular pacing in patients with congestive heart failure or bradycardia.
The process of implantation of an ICD is similar to implantation of a pacemaker. Like pacemakers, ICD devices are coupled to a set of leads containing electrode(s) and wire(s) which are passed though the vasculature to desired locations in the heart. For example an electrode can be passed through a vein to the right chambers of the heart, and then lodged in the apex of the right ventricle. Providing defibrillation pulses at this location has been found to be advantageous. As is the case with pacemaker leads, the leads are coupled to the header of the ICD and used to carry both stimulation pulses from the ICD to the heart and electrical signals from the heart to the ICD.
ICDs constantly monitor the rate and rhythm of the heart and can deliver therapies, by way of an electrical shock, when the electrical manifestations of the heart activity exceed one or more preset thresholds. More modern devices can distinguish between ventricular fibrillation and ventricular tachycardia (VT) and may try to pace the heart faster than its intrinsic rate in the case of VT, to try to break the tachycardia before it progresses to ventricular fibrillation. This is known as fast-pacing, overdrive pacing or anti-tachycardia pacing (ATP). ATP is only effective if the underlying rhythm is ventricular tachycardia, and is never effective if the rhythm is ventricular fibrillation.
Other IPG devices serve as neurostimulators and are used to treat pain, incontinence, and other neurologic and muscular conditions. Such IPG devices have a header used to couple the IPG to leads containing a plurality of wires and electrodes which deliver stimulating pulses from the IPG to nerves and muscles to provide beneficial therapies. The electrodes and wires of the leads may also be used to carry electrical signals back to the IPG.
The various types of IPG devices referenced above typically have a header to which the leads are attached. The header typically includes one or more bores each configured to receive a terminal pin of a lead. The terminal pin will typically contain a plurality of electrodes spaced along its length. Likewise, the bore will typically have a matching set of electrical contacts along its length which are spaced to form electrical connections with the electrodes of the lead pin. The electrical connections should be isolated from each other to prevent a short or unintended propagation of signals along a particular channel. The number and spacing or the electrodes and contacts may vary, but standards have emerged related to such numbers and such spacing for various types of stimulation systems.
Various types of electrical contacts have been employed in the headers of IPG devices. Prior art header designs often employed thin wire connections, female leaf springs, canted coil springs or “slide by” wire connectors. Many of these provided adequate electrical connection, but were fragile in design. Such connectors were easily damaged during pin insertion or incapable of producing mechanical forces sufficient to hold the pin in the desired orientation.
U.S. Pat. No. 4,934,367 granted to Daglow et al on Jun. 19, 1990 discloses the use of elastomeric rings either made of a conductive polymer or a non-conductive polymer impregnated with a conductive material. This and other patents also disclose the use of springs. For example, U.S. Pat. No. 6,895,276 granted to Kast et al on May 17, 2005 discloses a contact comprising a cylindrical housing comprising a wall having an inner surface defining a bore, a channel between the inner surface of the wall and the bore and a continuous spring fitted within the channel. U.S. Pat. No. 7,003,351 granted to Tvaska et al on Feb. 21, 2006 and U.S. Pat. No. 7,587,244 granted to Olbertz on Sep. 8, 2009 each show a connector with a similar ring having a plurality of spring contact members attached thereto. Further, U.S. Pat. No. 8,666,494 granted to Schramm et al discloses a spring contact ring comprising a housing including a recess channel and a spring comprising a base and a plurality of spring fingers.
Designing a connector for use in the header of an IPG device presents a variety of challenges which arise from the difficulty in maintaining the desired balance between mechanical and electrical properties. Examples of such challenges include: (1) limiting the mechanical insertion force required to insert the lead pin because excessive pressure exerted on the inner seal and electrical components of the bore can result in damage to the header; (2) excessive electrical engagement between the contacts of the header and the lead pin can result in shorts or faults which can draw off potential battery power; (3) insufficient mechanical retention forces can result in an electrode of the bore losing position or falling out of place; and (4) maintaining proper manufacturing tolerances. The tolerances of the electrode lead wires present further challenges with respect to the header's ability to achieve the desired electrical and mechanical responses. Thus, there continues to exist a real and substantial need to provide efficient and cost effective manufacturing methods and electrical contact designs for headers which meet these challenges.